Surface Modification Method for Solid Sample, Impurity Activation Method, and Method for Manufacturing Semiconductor Device

Abstract

The present invention intends to provide a method for manufacturing a semiconductor device in which source/drain extension regions having a uniform depth are created with high reproducibility. This objective is achieved by the following method: A gate electrode 24 is formed on a semiconductor substrate 21 via a gate insulator 23 . The portion of the semiconductor substrate 21 other than the gate electrode 24 is irradiated with an ultra-short pulsed laser light having a pulse width within a range from 10 to 1000 femtoseconds in order to create an amorphous layer 26 a . Then, recesses 27 are created in the semiconductor substrate 21 by selectively etching the amorphous layer 26 a . The recesses 27 are filled with semiconductor layers 28 whose impurity concentration is higher than that of the semiconductor substrate 21 , and the source/drain extension regions 31 are created there. Within the region other than the gate electrode 24 and the source/drain extension regions 31 , Deep diffusion layers 30 deeper than the source/drain extension regions 31 are created.

1 . A surface modification method for a solid sample, comprising a step of irradiating the solid sample with a pulsed laser light having a pulse width within a range from 10 to 1000 femtoseconds so as to modify only a surface layer of the solid sample from a crystalline phase to an amorphous phase or from an amorphous phase to a crystalline phase.  
   
   
       2 . The surface modification method for a solid sample according to  claim 1 , wherein 
 in a relationship between an ablation rate of the solid sample due to an irradiation of the pulsed laser light and a laser fluence of the pulsed laser light, a laser fluence value that gives a maximal value of a gradient of the ablation rate with respect to the laser fluence is identified as a threshold laser fluence; and    the solid sample is irradiated with the pulsed laser light with a laser fluence equal to or lower than the threshold laser fluence.    
   
   
       3 . The surface modification method for a solid sample according to  claim 1 , wherein the solid sample is made of a semiconductor material, and the semiconductor material is irradiated with an electromagnetic wave to excite valence electrons to a conduction band before an irradiation of the pulsed laser light.  
   
   
       4 . The surface modification method for a solid sample according to  claim 3 , wherein the aforementioned electromagnetic wave has a wavelength corresponding to an energy level higher than a band gap within the semiconductor material.  
   
   
       5 . The surface modification method for a solid sample according to  claim 1 , wherein the pulsed laser light is a circularly polarized light.  
   
   
       6 . An impurity activation method, wherein: 
 an impurity layer whose impurity concentration is higher than that of a semiconductor substrate is formed on the semiconductor substrate; and    the impurity layer is irradiated with a pulsed laser light having a pulse width within a range from 10 to 1000 femtoseconds in order to activate the impurity layer,    where a sheet resistance of the impurity layer after an irradiation of the pulsed laser light is controlled by changing irradiation conditions including the pulse width, a laser fluence and a number of pulse shots of the pulsed laser light.    
   
   
       7 . The impurity activation method according to  claim 6 , wherein: 
 in a relationship between the pulse width of the pulsed laser light and the sheet resistance of the impurity layer after the irradiation of the pulsed laser light, a gradient of the sheet resistance with respect to the pulse width changes at a specific threshold pulse width;    the gradient within a range below the threshold pulse width is larger than that within a range above the threshold pulse width; and    the impurity layer is irradiated with the pulsed laser light with a pulse width equal to or smaller than the threshold pulse width.    
   
   
       8 . The impurity activation method according to  claim 6 , wherein: 
 in a relationship between the laser fluence of the pulsed laser light and the sheet resistance of the impurity layer after the irradiation of the pulsed laser light, the sheet resistance takes a minimum value at the laser fluence; and    the impurity layer is irradiated with the pulsed laser light at a laser fluence that gives a substantially minimal value of the sheet resistance.    
   
   
       9 . The impurity activation method according to  claim 6 , wherein: 
 in a relationship between a number of pulse shots of the pulsed laser light and the sheet resistance of the impurity layer after the irradiation of the pulsed laser light, the sheet resistance takes a minimum value at the number of pulse shots; and    the impurity layer is irradiated with a pulsed laser light at a number of pulse shots that gives a substantially minimal value of the sheet resistance.    
   
   
       10 . The impurity activation method according  claim 6 , wherein the impurity layer is irradiated with an electromagnetic wave to excite valence electrons to a conduction band before the irradiation of the pulsed laser light.  
   
   
       11 . The impurity activation method according to  claim 10 , wherein the aforementioned electromagnetic wave has a wavelength corresponding to an energy level higher than a band gap within the semiconductor substrate.  
   
   
       12 . The impurity activation method according to  claim 6 , wherein the pulsed laser light is a circularly polarized light.  
   
   
       13 . The impurity activation method according to  claim 6 , wherein, when or before the impurity layer is formed, a semiconductor atom is added to or introduced into a region where the impurity layer is to be formed and the region is amorphized.  
   
   
       14 . The impurity activation method according to  claim 13 , wherein the semiconductor substrate is made of silicon and the semiconductor atom is silicon or germanium.  
   
   
       15 . A method for manufacturing a semiconductor device, wherein the device includes: 
 a gate electrode formed on a semiconductor substrate via a gate insulating film; and    an impurity-enriched source-side region and an impurity-enriched drain-side region, both formed on the semiconductor substrate so that the two regions face each other across a channel region at which the gate electrode is formed,    and the method includes:    an amorphous layer formation process in which an amorphous layer is created between the channel region and the impurity-enriched source-side region as well as between the channel region and the impurity-enriched drain-side region by casting a pulsed laser light having a pulse width within a range from 10 to 1000 femtoseconds;    a recess formation process for creating recesses in the semiconductor substrate by selectively etching the amorphous layer; and    a source/drain extension region formation process for creating source/drain extension regions by filling the recesses with semiconductor layers whose impurity concentration is higher than that of the semiconductor substrate.    
   
   
       16 . A method for manufacturing the semiconductor device, wherein the device includes: 
 a gate electrode formed on a semiconductor substrate via a gate insulating film; and    an impurity-enriched source-side region and an impurity-enriched drain-side region, both formed on the semiconductor substrate so that the two regions face each other across a channel region at which the gate electrode is formed,    and the method includes:    an impurity layer formation process in which impurity layers are formed by implanting an impurity element into a predetermined depth between the channel region and the impurity-enriched source-side region as well as between the channel region and the impurity-enriched drain-side region; and    an impurity layer activation process for activating the impurity layers by the impurity activation method according  claim 6.